Carrier current system



original Filed April 1, 1959 5 Sheets-Sheet l March 3, 1942 H. E. HERsHEY CARRIER CURRENT SYSTEM Original Filed April l, 1939 5 Sheets-Sheet 2 BY Mina/p1, M M

ATTORNEYS March 3, 1942.` H. E. HERsHEY CARRIER CURRENT SYSTEM Original Filed April l, 1939 3 Sheets-Sheet 3 HARRY E HERSHEY ATTORNEYS Patented Mar. 3, 1942 UNITED STATES PATENT OFFICE 'gipai application Api-ii 1, ms, serial No.

1940, Serial No. 330,979

3 Claims.

' The present invention relates to carrier current systems and, more particularly, to improvements in `systems wherein a power transmission line or the like is utilized as a control channel between a transmitting point and a plurality of control points. Carrier current apparatus utilizing power lines as carrier links has been extensively used for communication and control purposes and has been found to have particular utility in controlling from a central dispatchers station the connection of heater loads or the like to the power lines. This application is a division of application Serial No. 265,557, led April l, 1939.

It is an object of the present invention to provide an improved system of the character indicated which is of simple and economical arrangement; is reliable in operation and is arranged in an improved manner such that a large number of circuits or devices, such, for example, as water hea-ters, may be controlled from acentral dispatching or transmitting point with a minimum amount of apparatus.

It is a further object of the invention to provide. for use in a system of the character described, an improved receiving unit of simple and economical arrangement which is selectively controllable over an associated control channel to perform any desired one of a plurality of control operations with respect to any desired one of a plurality of associated circuits or devices which are to be controlled.

In general, the objects as set forth above are realized in accordance with the present invention by providing carrier current apparatus for controlling a plurality of secondary carrier current circuits arranged in groups,` and comprising a transmitter and a plurality of receivers which are interconnected by a carrier current channel so that the receivers are controlled over the channel from the transmitter in a novel and unique manner. More particularly, the transmitter includes a. carrier current source, a circuit for delivering current from the source to the carrier current channel, and apparatus 1ncludingV an impulsing device for momentarily interrupting the delivery circuit one or more times during each operation of the impulsing device thereby to transmit carrier current pulses by way of the channel to the various receivers. The transmitter further includes timing apparatus, the operation of which is initiated in response to operation of the impulsing device, and circuit means controlled by the timing apparatus for interrupting the carrier current delivery circuit transmitted over the carrier channel.

Divided and this application April 22,

after a predetermined time interval. The timing apparatus is so arranged that its operation is only initiated after a predetermined number of operations of the impulsing device and the operation thereof is sustained through the provision of relay means operable independently of the impulsing device following the initial operation of the timing apparatus. The arrangement of the transmitter is such that the timing apparatus may measure oiI either of two time intervals, during which carrier current is conducted to the associated carrier channel. The desired interval is selected through the selective operation of a pair of switches representing, respectively, heaters on and heaters off, and the provision of circuit means jointly controlled by these two switches and the timing apparatus for interrupting the carrier current delivery circuit at the end of the time interval corresponding to the operated one of the two switches.

The carrier current receivers commonly associated with the carrier current channel are each associated with a plurality of secondary carrier circuits which are to be controlled and each thereof includes apparatus responsive to a rst predetermined digit of carrier current pulses transmitted over the carrier channel for conditioning itself to select one of the associated secondary carrier circuits. This apparatus, as embodied in each receiver, is responsive to a rst digit other than the predetermined digit designating the receiver to render the receiver ineffective to select one of its associated circuits, or more particularly, to render the receiver nonresponsive to additional carrier current pulses Each receiver further comprises apparatus responsive to a second digit of carrier current pulses transmitted over the associated channel following the predetermined rst digit for selecting one of the associated secondary carrier circuits, together with circuit means controlled by the last-named apparatus for operating upon, i. e., for completing or interrupting the selected circuit. More particularly, each receiver includes a stepping switch having a plurality of operating positions individually corresponding to the associated secondary carrier circuits and pulse responsive apparatus which responds to a received iirst digit of carrier current pulses to cause the switch to operate to the position corresponding to the number of pulses of the digit. When each of the switches operates to a predetermined position (different for each of the receivers), the control apparatus associated therewith is conditioned for the selection of one of the associated circuits. Orr the other hand, if the switch is operated to any other position, it is rendered non-responsive to further operation of the pulse responsive apparatus. After being -conditioned to respond to a second serios of received carrier current pulses, each stepping switch and its associated control apparatus operates to select one of the associated secondary carrier circuits when the second digit of carrier current pulses is received. Thereafter. the 'control apparatus of the receiver functions to interrupt or complete the particular selected circuit. Each receiver is so arranged that when carrier current is removed from the channel over which it is controlled, the receiver is released and the operated control device is restored to normal.

Further features of the invention pertain to the particular arrangement of the circuit elements whereby the above-outlined andadditional operating features are attained.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figures 1 and 2 illustrate, respectively, a transmitter and a plurality of receiving units connected and arranged in accordance with the present invention and :interconnected by a carrier current channel; and Fig. 3 illustrates the apparatus which is controlled over one of the secondary carrier current channels.

Referring now to the drawings, the system there illustrated comprises a transmitter as shown in Fig. 1 and a plurality of receivers. two of which 1 are shown in Fig. 2; the transmitter and receivers being interconnected by a carrier current channel which includes one conductor I of a power transmission line and a ground return path. If desired a second of the power line conductors may be used in lieu of ground to provide a complete carrier current channel. Each of the receivers is arranged to control a plurality of control devices or units of the character shown in Fig. 3 over secondary carrier ,channels individually extending to these units. The carrier current output ofthe transmitter shown in Fig. 1 is impressed upon the carrier current channel comprising the conductor I0 and ground by means comprising a coupling unit II and a transformer I2. At each receiving station a coupling unit similar to the unit I I is provided for filtering the carrier current from the commercial frequency current and for delivering the filtered carrier current to the associated receiver. Thus, the receiver I3 and the other receiver illustrated in detail in Fig. 2' have individually associated therewith coupling units I4 and I5, respectively, which function to filter the carrier currents from the commercial frequency currents and to deliver the filtered output to the respective associated receivers. Each of the coupling units II, I I, and I5 may be of any desired arrangement. Since several well-known embodiments of this type of apparatus are commercially available, these elements of the system have been only schematically shown.

Referring now more particularly to the transmitting apparatus as shown in Fig. 1, this apparatus includes a source of carrier current comprising an alternator I6, arranged t0 deliver its actuaires' highl frequency output over an obvious circuit to the primary winding of a transformer I2 and to be driven by an alternating current motor I1 which is preferably of the selfstarting synchronous type. The motor I1 also functions to drive a self-excited direct current generator I8 which delivers exciting current to the slip rings of the generator I6 over any obvious circuit including the adjustable field rheostat I9'. This generator may also be utilized to supply current for energizing the various relays, magnets and signal lamps of the transmitter. To this end, the armature leads o1' the generator I8 are connected to bus terminals I9 and 2li which may, in turn, be connected over bus conductors to appropriate terminals of the indicated circuit elements. In the interests of simplifying the circuit explanation, these bus conductors have been omitted from the drawings but it will be understood that the negative terminal 20 is connected to each of the other terminals shown in Fig. 1 of the drawings marked with a negative battery sign and that the positive terminal I9 is similarly connected to each of the terminals designated by a positive battery sign. For the purpose of initiating the operation of the motor I1, there is provided a start key or switch 2 I, which switch also functions to control the operating circuit for a signal lamp 22 provided for the purpose of reminding the transmitter attendant or dispatcher that the switch 2I is operated'.

The circuit for delivering carrier current from the alternator I6 to the carrier channel comprising the power line conductor I0 and ground is arranged to be controlled by an electromagnetic device in the form of a pulsing relay or contacter 25 which is operative in response to operation of either of two key controlled switches 21 and 28. More particularly, the operating cir'- cuit for the pulsing relay 25 is completed in response to operation of either of two relays 3U and 40 which respectively respond to operation of the switches 21 and 28. These relays also individually control the operating circuits for a pair of signal lamps 23 and 24, the lamp 23, when energized, functioning to indicate that the relay is operated and the lamp 24, when energized, functioning to indicate that the relay is operated. The switches 21 and 28 selectively control the time interval during which carrier current is delivered to the carrier current channel and represent, respectively, heaters on and heaters off time intervals. Each of these switches is of the well-known nonlocking type. The above-mentioned operating circuit for the pulsing relay 25 also serially includes the pulsing springs 36 of an impulsing device 35. This impulsing device is of the dial operated type conventionally used in automatic telephone systems and is capable of transmitting from one to ten impulses during each operation through selective operation of the dial embodied therein. In addition to the pulsing springs 36, the impulsing device 35 includes a pair of shunt springs 31 which are operated into engagement each time the dial of the device is operated of! normal and are disengaged only following the return of the dial to its normal position. These shunt springs, in conjunction with the two relays 30 and 40, function to control the operation of the previously mentioned timing apparatus. More speciflcally, this timing apparatus -comprises a rotary stepping switch which is of conventional construction. This switch includes a single set of contacts 5I of twenty-,five points, a double-p.

ended wiper 52, and means comprising a motor magnet 33 and a ratchet and pawl mechanism, not shown, for driving the wiper 32 over the contacts of the set 3l. The mechanical arrange-` ment of the ratchet and pawl mechanism is such that the wiper 32 is advanced only upon deenergization of the magnet 33 following its energiza- Operatlon of the switch I from its normal position as shown in the drawings is initiated in response to operation of the impulsing device 3l. For the purpose of sustaining the operation of this switch following its initial or preliminary movement, there are provided a pair of relays 60 and 33; the iirst-mentioned being of the slow-tooperate type and the last-mentioned being of the well-known pendulum type. More particularly, the relay 65 includes a weighted armature 33 which vibrates when the relay 65 is initially energized and only settles into resting engagement with its associated contact a predetermined time interval thereafter. 'I'he switch E50 is arranged tocontrol a relay 10 which is provided for the purpose of causing the carrier current output of the .generator I3 to be removed from the carrier channel a predetermined time interval after operation of the switch 50 is initiated.

More particularly, the relay 10 is jointly controlled by the switch 50 and the relays 30 and 40 to cause the pulsing relay to restore a predetermined time interval after operation of the switch is initiated, providing the switch 21 is operated, or to 'cause the restoration of the pulsing relay 25 after the expiration of a longer time interval in the event the switch 28 is operated.

In order to cause the carrier current delivery circuit to be interrupted before either of the two indicated time intervals have expired and in the event of a dialing error on the part of the dispatcher, there is provided an error key 'l5 which, when operated, functions to complete a normalizing circuit for the rotary switch 50, thereby to cause this switch to be returned to its' normal position at a high rate of speed.

Referring now more particularly to Fig. 2 of the drawings, the two receivers there shown are, with the exception of certain wiring differences, exact duplicates. Accordingly, only one of the receivers has been illustrated in detail. The last-mentioned receiver functions to control ten associated circuits, one of which is indicated generally at 19. Each of these ten circuits is adapted to be energized by carrier current and may be utilized directly to control an associated control device or to control such a device over a secondary carrier channel. For example, if the f circuit 19 is to be used in an application of the character previously mentioned, that is, for the purpose of controlling the switching unit associated with an electric water heater, the switching unit may be directly connected to the bracketed terminals of the circuit 19 or may be coupled to these terminals over a carrier channel utilizing one or more of the secondary power unit illustrated in Fig. 3 of the drawings is of the character disclosed in Patent No. 2,064,644, granted December 15, 1936, to John L. Woodworth and comprises a switch 203 of the liquid contact type which is mounted on a control member 204 by means of spring clips 205 havlng registering apertures provided therein which engage portions of the metal hemispheres forming a part of the switch 203. The switch 203 may be of any desired commercial construction. One form of switch well adapted to this use comprises a pair of metal hemispheres separated by a flllet of thermoplastic insulating material which is fusion welded to the rims of the two hemispheres, whereby the container thus formed is sealed. A body of liquid conducting material such as mercury is sealed within the hemispheres and serves to make and break the electric circuit therebetween through an aperture provided in the fillet of insulated material when the switch is moved between two operating positions. The control element 204 is provided in its under-surface with an inverted Vshaped notch 206 which ts over the upperend of a resilient mounting member 201 to provide a pivot support for the element 204. The element 204 is biased for clockwise movement about its pivot' point by means of a spring 208, one end of which is anchored to the element 204 and the other end of which is anchored in the base of a slot provided in the resilient element 201. Thus the element 204 is biased for clockwise movement but, in the position shown, it is restrained against such movement due to the engagement of its right lower corner portion with the upper end of an actuating bimetallic thermal element 209. A heating coil 210 is provided for actuating the element 209 from its normal unflexed position to a flexed position. A reset trigger 2H having a hatch 2|2 formed therein and pivoted at 2l3 on the control element 204, cooperates with the free end of the element 209 to move the control member 204 between its two operating positions. The resilient mounting element 201 and the bimetallic thermal strip 209 are mounted on a supporting block 2N in any desired manner.

The switch 203 is included in the operating circuit for a heater load 2l5 which is arranged to be energized from the load current source over a. pair of feeder conductors 2I6 and 2H. For the purpose of controlling the position of the switch 203 in accordance with long and short carrier current pulses transmitted over the feeder conductors 2|6 and 2|1, there is provided a control circuit which comprises a condenser 2I3 and an inductance element 2I9 bridged across the conductors 2|6 and 241. These circuit elements have circuit constants which are so proportioned that they form series resonant circuit tuned to the frequency of the carrier voltage impressed on the circuit 19. This resonant circuit is arranged to control a relay 220 which includes a winding connected between a point 22| on the inductance element 2I9 and two additional points on opposite sides of the point 22| through rectifers 222 and 223 respectively. These rectiiiers are so polarized that uni-directional current is supplied through the winding of the relay 220 during both half cycles of the' alternating electromotive force appearing across the inductance 2|9 when carrier voltage is impressed upon the circuit 19. The relay 220 controls the energization of a transformer 224 which is arranged to be connected between the line conductors 2|6 and 2I1 and includes a secondary winding connected in series with the heating coil 2| 8. 2I8 for long and short periods, respectively, causes flexure of the thermostatic element 209 to operate the switch 283 between its opened and closed circuit positions, thereby to energize or de-energize the heater load 2I5.

Briefly described, the receiver illustrated in detail in Fig. 2 of the drawings comprises a rectifier 88 to which carrier current is delivered through the coupling unit I5 and which functions to convert the carrier current into direct current for energizing the combined start and pulsingrelay 85. If desired, the rectifier 88-may be of the well-known vacuum tube type utilizing Selective energization of the heating coil one or more stages of amplication for the purpose of increasing the amplitude of the received carrier current suilciently to insure positive response of the relay 85. In order to energize any selected one of the above-mentioned secondary carrier currentl circuits, there is provided at the receiving station a carrier current source which comprises a high frequency alternator 81 arranged to be driven by an alternating current motor 88, preferably of the self-starting synchronous type. The motor 88 is also mechanically coupled to drive a self-excited direct current generator 89 which functions to deliver exciting current through an adjustable ileld rheostat 98 to the slip rings of the alternator 81. It is also contemplated that the generator 89 shall be used to supply energizing current to the windings of the various relays and magnets embodied in the receiver. To this end, the-positive and negative terminals 9| and 92, respectively, of the generator 89 are connected by means of bus conductors, not shown, to the respective positive and negative terminals of the relay and magnet windings shown in Fig.l 2 of the drawings. The alternating current motor 88 is adapted to be energized from the usual 110 volt alternating current source and includes an operating circuit which is controlled by an alternating current relay or contactor 95. This contacter, in turn, is controlled by an alternating current relay 91 having a winding adapted to be connected in shunt with the secondary winding 99 of a voltage reducing transformer |88 in series with a condenser |8I, in response to operation of the combined start and pulsing relay 85.

For the purpose of selecting one of the ten associated secondary carrier circuits, there is also provided in the receiver illustrated in Fig. 2 a circuit selecting switch |85 and control apparatus comprising a plurality of relays I38 |48, |58, |60, |18, |88 and |98. More particularly, the switch |85 is of the well-known rotary type and comprises four sets of contacts |86, |81, |88 and |09, each comprising eleven contacts; wipers H8, ||2 and. ||3 respectively associated with the contacts sets in the order named; means comprising a motor magnet H4 and a ratchet and pawl mechanism, not shown, for driving the indicated wipers over their respectively associated contacts; and a set of off-normal springs I5 which are moved into engagement when the wipers of the switch are stepped to the first oinormal position from the normal position illustrated in the drawings. Of the enumerated relays, the relay |30 is a highly sensitive pulsing relay which responds to operation of the combined start and pulsing relay 85; the relay |48 is a slow-acting hold'relay; the relay |58 is a slave to the relay |48 and the relay |68 is a slowacting pulsing digit responsive relay. 0f the remaining three relays the relay |98 is provided for the purpose of rendering the switch responsive to a second digit of received carrier current pulses following the receipt of a first digit designating the receiving unit under 'consideration as the one receiver which is to effect a circuit controlling operation. This relay further functions to cause the wipers of the switch |85 to be returned to normal during the interdigit pause between two successively received digits. The relay |80, in combination with the slow-to-operate relay |18, functions to open the operating circuits for the motor magnet IM at the end of a received second digit of carrier pulses, thereby to render the receiver non-responsive to additional pulses received after a circuit selecting operation has been performed. In this regard it is pointed out that control of the ten secondary carrier circuits associated with the receiver is achieved through the provision of ten control devices, one of which is indicated at 288, which individually correspond to the ten operating positions of the switch |85 and individually include operating circuits extending by way of different ones of the contacts embodied in the contact set |89 of the switch |85. 'I'he manner in which these operating circuits are selectively completed will be more readily apparent from the description of the operation of the apparatus appearing hereinafter.

Referring now more particularly to the operation of the system, if it be assumed, for example, that the control device or switch 283 controlled by way of the secondary carrier circuit 19 occupies its open circuit position, and, further, that the dispatcher or attendant desires to effect operation of this control device to close the associated heater or load circuit, the switch 2| is rst operated to its off-normal position and shortly thereafter the switch 21 is also operated to its off-normal position. When the switch 2l is operated to its off-normal position, obvious circuits are completed for energizing the motor I1 and the signal lamp 22. As the motor I1 comes up to speed, the voltage across the terminals I9 and 28 of the generator I8 builds up to normal so that with the field rheostat I9 properly adjusted the correct exciting current is supplied to the rotor of the alternator I6. Accordingly, the carrier voltage of this generator builds up to the normal value in the usual manner. Following the interval required for the motor I1 to assume its normal speed, the switch 21 is momentarily operated to its off-normal position to complete an obvious circuit for energizing the relay 38. Upon operating, the relay 38 completes, at its armature 3|, an obvious circuit for energizing the signal lamp 23 and closes, at its armature 32, a circuit including the armature 1| for maintaining itself energized independently of the switch 21. Hence, momentary operation of the switch 21 suffices to initiate the operation of the transmitter. Upon operating, the relay 38 also completes the above-mentioned circuit for energizing the winding of the pulsing relay or contactor 25, this circuit extending from the positive terminal I9 of the generator I8 by way of the winding of the relay 25, the armature 33 and the impulsing springs 36 to the negative terminal 28 of the generator I8. When energized over this circuit, the relay 25 operates to complete at its armature 26 the circuit for energizing the primary winding of the transformer I2 from the alternator I6. Thus. carrier current voltage is impressed upon the carrier channel comprising th conductor and ground, which channel extends from the transmitter to each of the receivers controllable from the transmitter.

The rectifier 80 provided in the receiving unit illustrated in detail in Fig. 2 responds to the carriercurrent voltage impressed upon the carrier channel by delivering direct current to the winding of the combined start and pulsing relay 85. The relay 85 now operates to complete, at its amature 86, a circuit including the transformer winding 99 and the condenser |0| for energizing the alternating current relay 91. The relay 91, in turn, operates to complete at its armature 98 an obvious circuit for energizing the winding of the contactor 95. This contactor, upon operating, completes at its armature 96 an obvious circuit for energizing the alternating'current motor 88.. As the motor 88`comes up to speed, the normal output voltage of the direct current generator 89 is built up across the generator terminals 9| and 92 and eld current is supplied to the rotor of the alternator 81. Thus, the carrier voltage output of the alternator 81 is built up to its normal value. When the voltage of the generator 89 assumes its normal value, the relay |30 is energized thereby over a circuit extending from the positive generator terminals 9| by way of the armature 86 and the winding of the relay |30 to the negative generator terminal 92. When thus energized, the relay |30 operates to complete at its armature |3| an obvious circuit for energizing the slow-acting hold relay |40. The last-mentioned relay, in turn, operates to complete at its armature III an obvious circuit for energizing the relay |50. When the relay |50 operates, it prepares at its armature |5| a circuit for energizing the slow-acting relay |60 and the motor magnet ||4 in parallel. At its armature |52, the relay |50 prepares a point in the common portion of the holding and operating circuits, traced hereinafter, for the relays |10, |80 and |90. At its armature |53, the relay |50 completes an obvious multiple circuit for maintaining the/contactor 95 operated. Finally, at its armature |54, the relay |50 prepares a point in the common 4portion of the operating circuit for the control device 200 and the operating circuits for each of the other nine control devices associated with the receiver. Following the operation of the relay |50, the receiver illustrated in Fig. 2 is conditioned to respond to carrier current pulses transmitted by way of the carrier channel from the transmitter shown in Fig. 1 in response to operation of the impulsing device 35.

While the operation of the receiver shown in detail in Fig. 2 has alone beendescribed, it will be understood that each of the other receivers associated with the carrier channel comprising the conductor |0 and ground responds to the application of carrier voltage to this channel in an identical manner.

A short time interval after operation of the switch 21, and shortly following the completion of the receiver operations just described, the transmitter attendant operates the impulsing device 35 in accordance with the digit designating the receiver associated with the group of circuits including the particular circuit which is to be operated upon. In the case under consideration, wherein the circuit 19 is to be operated upon, the attendant dials a first digit of six impulses. During the forward movement of the dial embodied in the impulsing device 35 and immediately the`dial is moved ot! normal, the shunt springs 31 are moved into engagement to complete a circuit for energizing the operating magnet 53 of the minor switch 50, this circuit extending from the positive generator terminal I9 by way of the armature 34, the shunt springs 81 and the winding of the magnet 53 to the negative generator terminal 20. When energized over this circuit, the magnet 53 conditions the associated ratchet and pawl mechanism, not shown, to step the wiper 52 one step from its normal position as shown in the drawings. During the return movement of the dial embodied in the impulsing device 35, the pulsing springs 36 are opened and closed a number of times determined by the number of the digit dialed. In the case under consideration, these springs are opened and closed six times. Each time the springs 36 are moved out of engagement, the above-traced operating circuit for the relay 25 is interrupted, causing this relay to restore and open at its armature 26 the circuit over which carrier current is delivered to the carrier current channel. Accordingly, during the first operation of the impulsing device 35, six carrier current pulses are .transmitted over the channel to each of the receivers associated therewith. At the end of the, sixth impulse, the dial of the impulsing device 35 is fully restored to normal, so that the springs 36 are closed and the shunt springs 31 are moved out of enegagement to interrupt the above-traced circuit for energizing the magnet 53. As a consequence,the ratchet and pawl mechanism associated with the magnet 53 operates to advance the wiper 52 one step from normal'or into engagement with its associated first contact.

Considering now the manner in which the receiver illustrated in detail in Fig. 2 responds to the carrier current pulses of the first digit dialed at the transmitter, it is pointed out that the relay 85 follows the carrier current pulses by restoring during each interval when the carrier current delivery circuit is interrupted at the transmitter. Accordingly, it will be seen that the relay 85 functions to repeat the carrier current pulses as direct current pulses to the pulsing relay |30, the relay |30 being caused to restore each time the carrier current delivery circuit is interrupted at the transmitter. Upon restoring at the beginning of the first pulse, the relay |30 completes the above-mentioned circuit for energizing the slow-acting relay |60 in parallel with the motor magnet of the rotary switch |05, this circuit extending from the positive generator terminal 9| by way of the armature |3| to the armature |5| where it divides; one branch extending through the winding of the relay |60 to the negative generator terminal 92, and the other branch extending by Way of the armature |1| and the winding of the magnet ||4 to the negative generator terminal 92. When energized over the circuit just traced, the relay |60 operates to open at its armature |6| a point in the circuits, traced hereinafter, for energizing the relays |10 and |90, respectively. At its armature |62, the relay circuits for energizing the control devices cor- |60 opens a point in the common portion of the responding to and including the device 200.

Each time the relay |30 restores in response to a received carrier pulse to complete the abovetraced circuit for energizing the motor magnet Ill, this magnet in cooperation with its associated ratchet and pawl mechanism, not shown, operates to advance the Wipers of the switch |05 one step. Accordingly, at the end of the first digit, these wipers are. left standing in engagement with the contacts corresponding to the number of pulses of the digit. The relay |60, due to its slow-to-release character, remains operated during pulsing. When the wipers of the switch |05 are operated to their respective first ofi-normal positions, the off-normal springs ||5 are moved into engagement to prepare a circuit, traced hereinafter, for energizing the slow-tooperate relay 10. In the case under consideration wherein rst digit dialed comprises six carrier current pulses, the wipers of the switch are left standing in engagement with their respectively associated sixth contacts. Shortly following the end of this digit and with the, relay i90 in its operated position, the slow-acting relay itil restores to complete the above-mentioned circuit for energizing the relay |99, this circuit extending from the positive generator terminal 9| by way of the armature |52, the ar-'mature itl, the wiper i I2 and its associated sixth contact, the contact |95, the armature |93, and the winding of the relay |90 to the negative gen.- erator terminal 92. When energized over the circuit just traced, the relay |90 operates to complete a holding circuit for itself, this circuit extending from the positive'generator terminal 9| by way of the armature |52, the armature |94, the armature l93, and the winding of the relay |90 to the negative generator terminal 92. Also, upon operating, the relay |90 opens at its armature |96 a point in the circuit, traced hereinafter, for energizing the slow-to-operate relay |10, and prepares at its armature |92 a circuit for energizing the relay |80. At its armature |9|, the relay |90 completes an alternative circuit for energizing the motor magnet ||4, this circuit ex.- tending from the positive generator terminal 9| by way of the armature |9|, the armature |8|l, the multipled contacts of the Contact set |06, the wiper |i0, the armature ||6 and the winding of the magnet l lf3 to the negative generator terminal 92. Due to the circuit interrupting action of the armature |||S controlled by the magnet H4, this magnet operates buzzer fashion rapidly to restore the wipers of switch |05 to normal at which time the off-normal springs I5 are opened. When the wiper attains its normal position in engagement with its associated eleventh contact, the above-traced normalizing circuit for the switch is interrupted. The return of the switch wipers to normal also results in energization of the relay |80 over a circuit extending from the positive generator terminal 9| by way of the armature |52, the wiper and its associated eleventh contact, the armature |92 and the winding of the relay |80 to the negative generator terminal 92. Upon operating, the relay |80 completes, at its armature |82, an obvious locking circuit for itself, and opens, at its armature |8 I, a further point in the above-traced switch normalizing circuit. At its armature |83, the relay |80 prepares the above-mentioned circuit for er1- ergizing the slow-to-operate relay |10. Following operation of the relay |80, the apparatus embodied in the receiver illustrated inv detail in Fig. 2 of the drawings is conditioned to respond to a second series of carrier pulses transmitted thereto from the transmitter shown in Fig. 1 of the drawings.

The circuit group or receiver selection achieved in response to the rst digit dialed at the transmitter is obtained by connecting the relays, corresponding to the relay |90 and included in the other receivers, to be energized in response to operation of their respectively associated rotary switches to different off-normal positions. In this regard, it will be clear from the preceding i description that the rotary switches respectively embodied in the several receivers areoperated in unison in response to the carrier current pulses of the rst digit. Only the relay i of the receiver shown is, however, connected to be energized when the wipers of these switches are left standing in engagement with their respectively associated sixth contacts at the end of the iirst digit. The corresponding relays of the other receivers are connected to be energized when the wipers of the respectively associated rotary switches are left standing .in engagement with other contacts at the end of the rst digit of carrier current pulses. For example, the relay embodied ln the receiver i3 and corresponding to the relay i90, may be connected to be energized when the rotary switch of this receiver is operated to its second oir-normal position in response to the carrier current pulses of the first digit. As a further example, a third of the receivers may be so connected and arranged that the relay embodied therein and corresponding to the relay |90 is energized following the transmission of a first digit comprising three carrier current pulses. By virtue of this arrangement, any one of ten different receivers may, with the arrangement shown, selectively be conditioned to respond to the carrier pulses resulting from the dialing of a second digit at the transmitter.

To illustrate the manner in which a receiver is rendered non-responsive to further carrier current pulses when a rst digit other than the digit designating the receiver is dialed at the transmitting station, the response of the receiver illustrated in Fig. 2 to a first digit comprising three impulses may be considered. In this case, the wipers of switch E05 are left standing in engagement with'their respectively associated third contacts at the end of the digit. Accordingly,

the operating circuit for the relay i90 is not completed. Since this relay fails to operate, the operating circuit for the slow-to-operate relay E19 is energized for a substantial time interval during the .inter-digit pause between the rst and second digits. This circuit is completed in response to the restoration of the relay |60 and may be traced as extending from the positive generator terminal 9| by way of the armature |52, the armature i6 the off-normal springs i5, the armature |96 and the winding of the relay |10 to the negative generator terminal 92. After anY interval following the completion of this circuit, the relay |10 operates to complete, at its armature |12, an obvious holding circuit for itself. At its armature |1|, the relay |10 opens a` point in the above-traced circuit for energizing the motor magnet ||4 of the rotary switch |05. Thus, this rotary switch is rendered non-responsive to further carrier current pulses transmitted to the receiver. Since the relay |90 fails to operate, the wipers of the switch |05 are left standing in their third off-normal positions until carrier current is removed from the carrier channel to initiate the release of the receivers in the manner explained subsequently. Since the operating circuit for the relay |90 extends only by way of the sixth contact of the contact set |08, it will be apparent that the operations just described occur in any case when a iirst digit other than the digit six is dialed at the transmitter. It; willful-ther be apparent that since any one of ten different digits comprising from one to ten pulses may be dialed at the transmitter any one of ten diierent receivers may be conditioned, to the exclusion of all of the other receivers, to respond to the pulses of the second digit.

The character of the second digit dialed at the transmitter depends upon the particular one of the secondary carrier circuits which is to be operated upon. In the present case wherein the circuit 19 is to be completed and the control device 200 associated with this. circuit can only be energized by way of the tenth contact of the contact set |09, a second digit of ten impulses is dialed at the transmitter. The receiver illustrated in Fig. 2 of the drawings responds to the carrier current pulses of the second digit in a manner substantially similar to that just described with reference to the carrier current pulses of the rst digit. More` particularly, the

relay |30 follows the carrier current pulses and transmits corresponding pulses to the motor magnet ||4 of the switch |05 so that the wipers of this switch are advanced to the olf-normal position corresponding to the number of pulses making up the second digit. Also, the relay |60 operates at the beginning of the first pulse of the digit and due to its slow-to-release characteristic, remains operated until the digit is ended. Further, the olf-normal springs ||5 are closed to prepare the circuit for energizing the relay when the wipers of the switch |05 are operated to their respective flrst off-normal positions. In the present case wherein ten carrier current pulses are transmitted to the receiver during the dialing of the second digit, the wipers of the switch |05 are left standing in engagement with their respectively associated tenth contacts when the digit is terminated. Shortly after the last carrier pulse is received and with the relay |30 operated, the relay |60 restores to complete an alternative circuit for energizing the slow-tooperate relay |10, this alternativegcircuit extending from the 4positive generator terminal 9| by way of the armature |52, the armature |6|, the olf-normal springs I5, the armature |83, and the winding of the relay |10 to the negative generator terminal 92. Upon restoring, the relay |60 also completes the operating circuit for the control device 200 associated with the selected secondary carrier circuit 19. This circuit may be traced as extending from one terminal of the alternating current source by way of the winding of the control device 200, the tenth contact of the contact set |09, the wiper ||3 andthe armatures |84, |62, and |54 to the opposite terminal of the alternating current source. When energized over this circuit, the control device 200 operates to complete at its armature the secondary carrier circuit 19, whereby carrier current is transmitted from the generator 81 over the circuit 19 and the secondary carrier channel 202 to energize the series resonant circuit comprising the condenser 2 i8 and the inductance element 2|9. Following the operation of the control device 200, no further operations occur in the receiver until carrier current voltage is removed from the carrier channel comprising the conductor lnd ground.

When the series tuned circuit comprising the inductance element 2|9 and the condenser 2|8 is energized, current is caused to flow through the rectifying elements .222 and 223 and the winding of the relay 220. This relay in operating, completes an obvious circuit for energizing the transformer 224 whereby heating current is lsupplied to the heating coil 2|0, causing the therresilient element 201. In response to this move-y ment of the control element 204, a circuit is established through the switch 203 for energizing the heater load 2|5. If the carrier voltage impressed on the circuit 19 is now interrupted, the control element 204 remains in its operated position due to engagement of the free end of the element 209 with the right lower corner portion of the control element 204. Thus the circuit including the load 2 5 remains in an energized condition.

During operation of the impulsing device 35 to cause the second digit of ten carrier pulses to be transmitted over the carrier channel, the shunt springs 31 are moved into engagement to again complete the above-traced operating circuit for the operating magnet 53. At the end of the digit and when the dial embodied in the impulsing device 35 returns to normal, the indicated shunt springs are moved out of engagement to interrupt the operating circuit for the magnet 53, thus permitting the ratchet and pawl mechanism associated with this magnet to advance the wiper 52 a second step or into engagement with its associated second contact. With the wiper 52 in this position a circuit is completed for energizing the pendulum type relay 65, this circuit extending from the positive generator terminal I9 by way of the winding of the relay 65, the second contact of the Contact set 5|, the wiper 52, the armature 54, and the winding of the magnet 53 to .the negative generator terminal 20. Due to the relatively high resistance of the winding of the relay 65, the magnet 53 is insuiiciently energized over the circuit just traced to operate. The relay 65, however, attracts its associated armature 66 which, due to the weight carried by the free end thereof, starts to vibrate, intermittently to complete an obvious circuit for energizing the slow-to-operate relay 60.1 After a predetermined and substantially fixed time interval, the vibration of the Weighted armature 66 dies out and this armature settles into engagement with its associated working contact, thereby to maintain the relay 60 continuously energized. A sort time interval thereafter, the slow-to-operate relay 60 operates to complete at its armature 6| an obvious alternative circuit for energizing the magnet 53. This magnet now operates to condition the associated ratchet and pawl mechanism to step the wiper 52 a third step and to open at its armature 54 the abovetraced circuit for energizing the relay 65. As a result, the two relays, 65 and 60, sequentially "restore in the order named, the last-mentioned circuit thereof, functioningto open at its armature 6| the alternative circuit for energizing the magnet 53. When the magnet 59 is deenergized, the wiper 52 is advanced to its third off-normal position and the armature 54 is released to recomplete the above-traced operating circuit for the relay 65. Since the second to eighth contacts of the contact set 5| are multipled together, the cycle of operations just described and involving the two relays 60 and 65 and the magnet 53, is repeated seven times. When the wiper 52 is stepped to its ninth off-normal position or into engagement with its associated ninth contact., a circuit is completed for energizing the relay l0, this circuit extending from the positive generator terminal I9 by way of the winding of the relay 10, the armature 44, the ninth contact of the contact set 5I, the wiper 52, the armature 54, and the winding of the magnet 53 to the negative generator terminal 20. Due to the relatively high resistance of the winding of the relay 10, the magnet 53 is insuiiiciently energized to operate when the circuit Just traced is completed. The relay 10, however, operates to open at its armature 1| the previously traced holding circuit for the relay 30, causing the last-mentioned relay to restore. Upon restoring, the relay 30 opens, at its armature 3|, the circuit for energizing the signal lamp 23, and interrupts, at its armature 33, the circuit over which the contactor 25 is being held energized. The contactor 25 now restores to open the circuit over which the carrier current voltage of the alternator i6 is being impressed upon the carrier channel comprising the conductor I and ground. The relay '|0, upon operating also completes, at its armature 1|, an obvious alternative circuit for energizing the magnet 53. This magnet in turn attracts its armature 54 to open the operating circuit for the relay 'Ilcausing this relay to restore and open the operating circuit for the magnet 53. The ratchet and pawl mechanism associated with this magnet now advances the wiper 52 into engagement with its associated tenth contact. When the wiper 52 is stepped to its tenth off-normal position, a switch normalizing circuit is completed for energizing the magnet 53. This circuit may be traced as extending from the positive generator terminal I9 by way of the armature 43, the multipled tenth to twenty-second contacts of the contact set the Wiper 52, the armature 54, and the winding of the magnet 53 to the negative generator terminal 20. Due to the circuit interrupting action of the armature 54, the magnet 53 is repeatedly energized over the circuit just traced to cause the wiper 52 to be driven toward its home position. Since the twentyfourth contact of the contact set 5I is connected directly to the positive generator terminal I9 and the twenty-third contact of the contact set 5| is connected to this generator terminal over a path including the restored armature 42 of the relay 40, the stepping operation of the switch 50 occasioned by energization of the magnet 53 over.

the normalizing circuit just traced, continues until the wiper 52 is returned to its home position. When this occurs the switch normalizing circuit is interrupted. Also, when the wiper 52 is disengaged from the multipled second to eighth contacts of the contact set 5I, the operating circuit for the relay 65 is interrupted. Ac-

cordingly, the two relays 65 and 60 are deenergized. Thus, all of the relays embodied in the transmitter shown in Fig. 1 of the drawings are restored to normal. When the attendant observes the deenergized condition of the signal lamp 23 he is informed that the desired control operation has been completed and he may then restore the start key 2| to its normal position to arrest the operation of the motor I'| and the generators I5 and I8 driven thereby. Also, when the start key 2| is returned to normal, the operating circuit for the signal lamp 22 is interrupted and this lamp is deenergized. Thus, the transmitter is fully released.

When the carrier current voltage is removed from the carrier channel comprising the con.-

ductor I0 and ground, the relay 85 embodied in the receiver illustrated in detail in Fig. 2 is deenergized and restores. In a similar manner the corresponding relays embodied in the other receivers coupled to the carrier channel also restore. Upon restoring, the relay initiates the sequential restoration of the relays 0l, |30, i 40, and |50 in an obvious manner. With the two relays 91 and |50 deenergized, the operating circuit for the contactor 55 is interrupted causing this contactor to open, at its armature 55, the operating circuit for the motor Bil. Accordingly, operation of the motor Bt and the two generators 8l and 89 are arrested. When the relay E50 restores, it opens, at its armature lili, a point in the common portion of the operating and holding circuits for the three relays H0, and. causing any operated ones of these relays to restore. Upon restoring, the relay I5@ also functions to interrupt at its armature i5@ the abovetraced operating circuit for the control device 200, whereby the last-mentioned device is released to interrupt the secondary carrier current circuit '19. At its armature .|5I, the relay lii, upon restoring, completes an alternative circuit for energizing the motor magnet IM of the switch |05, this circuit extending from the positive generator terminal 9| by way of the armature I3I, the armature I5I, the multipled rst to tenth contacts of the contact set |06, the wiper IIO, the armature H6 and the winding of the magnet H4 to the negative generator terminal 92. Due to the circuit interrupting action of the armature IIS, the motor magnet Itri operates buzzer fashion rapidly to return the wipers of the switch I05 to their respective normal position at which time the off-normal springs II5 are opened. When the wiper H0 is returned to its normal position, the switch normalizing circuit just traced and including the armature I I6 is interrupted. Thus, the wipers of the switch |05 are left standing in their respective normal positions. In connection with the restoration ci the switch |05 to normal, it will be noted that the switch normalizing circuit is initially completed substantially simultaneously with the deenergization of the driving motor 80 for the generator 89. Due to the mechanical inertia of the moving system driven by the motor 88, however, the voltage developed by the generator 89 is suiiicient to enable the switch normalizing operation of the rotary switch |05 to be fully effected before the voltage of the generator 89 drops to an abnormally low value.

Although the release of the receiver shown in detail in Fig. 2 has alone been considered, it will be understood from the description pertaining to this receiver that the other receivers coupled to the carrier channel are restored to normal in an identical manner.

In the event the dispatcher attending the transmitter shown in Fig. 1 desires to cause a switching unit associated with one of the secondary carrier channels to be operated to the open circuit position, the key 28 is actuated-.nto its offnormal position instead of the key K2`II following operation of the start switch 2|. For example, if the dispatcher desires to operattathe control device or switch 203 to its open circuit posi- 4 ergiaing the relay 4I. The relay 4I performs the same operations as arefdescribed above with reierence to the relay Il, i. e., it vcompletes-at its v armature 40 the previously traced circuit for en- .ergizing the contacter 2l, prepares at its armature 41. the circuit for energizing the operating magnet Il of the switch Il and completes at its amature 4l a holding circuit i'or itself. In addition, the relay 40 completes at its amature 4| an obvious circuit for energizing the signal lamp .24, opens at its amature 44 a point in the pren viously traced operating circuit for the relay 10,

and prepares at its armatureV 42 an alternative -operating circuit for the last-mentioned relay.

At its amature 44, the relay 40 also impresses positive generator potential upon the ninth contwo to eight inclusive, of the indicated contact set. 'I'he purpose of the operations just described is to insure that the relay 10 will not be operated until the wiper 52 of the switch 50 is moved, under the control of the relays i and 85 and the operating magnet 53, over the associated contacts numbered from two to twenty-two inclusive. Such movement oi' the wiper 52 obviously requires a considerably greater time interval than that required for movement of the wiper over the contacts numbered from two to eight inclusive, of the contact set 6|. This, of course, means that carrier current is maintained upon the carrier channel comprising the conductor i0 and ground, for `a. considerably longer time interval than in the case when the relay 20 was operated in response to operation of the key 21. Specifically, the arrangement is such that when the key 21 is operated to cause the operation ofthe relay 30, carrier current is conducted to the carrier channel for a period or ten seconds iollowing the completion of the dialing operation; whereas when the key 20 is operated to cause the operation of the relay 40, carrier current is conducted to the carrier channel for twenty seconds following the completion of the dialing operation at the transmitter.

After the keye24 is operated to its off-normal position to perform the function just described,

the impulsing device 35 is actuated in the manner previously explained and in accordance with the two digits designating the secondary carrier circuit to be operated upon. The manner in which the receivers associated with the carrier channel respond to the carrier pulses is exactly the same as set forth above with reference to operation of the impulsing device 35 following operation of the key 21. Here again, since the circuit 10 is to be completed. the-control device 200 is energized over the previously traced circuit shortly following the conclusion of the second digit. Also, at the end of the second digit, sustained operation of the rotary switch 50 is maintained through the above-described inter-action between the operating magnet 53 and the tw'o relays 60 and 65. The stepping operation of the rotary switch 50 under the control of the indicated relays continues until the wiper of lthis switch is moved into engagement with the ninth contact of the contact set at which time, a circuit independent of the relays 60 and 65 is completed for energizing the operating magnet Il. This circuit extends frorfnthe positive genment with its associated twenty-third contact,y the above-mentioned alternative circuit is completed for energizing the relay 10. this circuit extending from thepositive generator terminal il by way of the winding of the relay |II, the

erator terminali! by way'of'the armature 44,` l

the ninth contact of the contact set Il, the wiper v l2, the armature I4 andthe winding of the 4magnet Il to the negative generator terminal 20.

control of the two relays 00 and 0l. 'Ihereai'ten and when the wiper 52 is stepped into engagearmaturev 42, the twenty-third contact of the contact set Il, the wiper 52, the armature 04.

and the winding of the magnet B3 to the nega` tive generator terminal 20. -When the relay 10 operates, it initiates the release of the transmitter and of the various receivers coupled to the carrier channel in the exact manner previously described. During this release of the apparatus, the control device 200 is deenergized to interrupt at its armature 20|, the selected secondary carrier current circuit 10. Also, during the release of the apparatus and when the relay 10 oper-v ates, the holding circuit for the relay is interrupted causing the last-mentioned relay to restore to open the operating circuit for the signal lampv24l and to restore the normal circuit connections associated with the contact bank of the rotary switch 50. Upon operating, the relay 'l0` also completes the previously traced alternative circuit for energizing the magnet 53, wherebyv this magnet is caused to restore the wiper I2 202, the relay 220 is operated to complete thecircuit for energizing the heating coil 2|0. In this case the circuit for energizing the heating coilisheld completed for a substantially longer v time interval than that required to operate'the switch 202 to its closed circuit position. During this interval the thermostatic element 209 is the relay 220 is deenergized and restores to deenergize the heating coil 2|0 with the result that the thermal element '200 is cooled. As this element cools the free end thereof is moved to the left and during such movement rides in the slot 2|2 formed in the trigger 2l I. Due to the toggle action between the trigger 2| i, the thermal element 209 and the control element 204, the last mentioned element is returned to its normal horizontal position and the free end of the thermal element 209 is again moved beneath the right lower corner of the control element 204 to restrain the latter element in its normal position. As the control element 204 is returned to normal, the circuit for energizing the heater load 2|5 and established through the contacts of the switch 203, is interruptedil-e As previously indicated,fthe error key 15 is provided for the purpose of rapidly normalizing the apparatus in the event the dispatcher, after partially performinga circuit control'selecting operation, discovers an error in his procedure. For example, if the dispatcher discovers, after dialing the first digit of a circuit designating number, that he has dialed the wrong digit or that he has operated the wrong one of the two keys, 21 and 28, he may operate the error key 15 and cause the apparatus to be restored to normal before any of the secondary carrier current circuits have been affected. When the key 15 is operated to its off-normal position, positive generator potential is impressed by way of the switch springs 16 and 11 directly upon the first and the multipled second to eighth contacts of the cointact set I. Also, if the relay 40 is the operated one of the two relays 30 and 40, positive generator potential is impressed by way of the springs 'I1 upon the multipled tenth to twentysecond contacts of the contact set 5I. Alternatively, if the relay 30 is the operated one of the two relays 30 and 40, positive generator potential is impressed upon the last-mentioned contact multiple over the previously traced path, including the restored armature 43 of the relay 40. Immediately the above described paths are completed, the operating magnet 53 of the switch 50 is energized over the switch normalizing circuit including the circuit interrupting armature 54. As a result, the wiper 52 is rapidly driven to its normal position. During such movement of the wiper 52, one of the two previously traced circuits is completed for energizing the relay 10, which relay upon operating, initiates the release of the apparatus in the exact manner previously described.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is contemplated to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A receiver adapted to be controlled over a control channel to control a plurality of associated circuits and comprising, in combination, a switch having a normal position and operative to a plurality of off-normal positions individually corresponding to said circuits, means responsive to a first predetermined digit of current pulses transmitted over said channel for causing said `switch to operate to one of said off-normal positions, means for rendering said switch nonresponsive to further operation of said firstnamed means, means responsive to operation of said switch to said one off-normal position for preventing said last-named meansfrom operating and for causing said switch to operate to its normal position, said first-named means being operative to cause said switch to operate to the off-normal position corresponding toa desired one of said circuits in response to a second digit of current pulses transmitted over said channel following said predetermined digit, and means responsive to the last-mentioned operation of said switch for operating upon said one -digit of current pulses transmitted over.said

channel for causing said switch to operate to one of its off-normal positions, means for rendering said switch non-responsive to further operation of said first-named means, means responsive to operation of said switch to said one position for preventing said last-named means from operating and for causing said switch to operate to its normal position, means responsive to the lastmentioned operation of said switch to its normal position for preparing all of said operating circuits, said first-named means being operative to cause said switch to operate to the off-normal position corresponding to a desired one of said control devices in response to a second digit of current pulses transmitted over said channel following said rst digit, thereby further to prepare the operating circuit for said one control device, and means operative following the lastmentioned operation of said switch for completing the operating circuit for said one control device.

3. In a system for selectively controlling a plurality of circuits and which includes a selector controllable by a transmitting device provided at a remotelylocated control station to select one of said circuits and control means for operating` upon the selected circuit; switching means at said control station having two different settings, timing means at said control station and operative in response to the operation of said transmitting device to measure either of two different time intervals depending upon the setting of said switching means, and means controlled by said timing means for releasing said control means at the end of the measured time interval.

HARRY E. HERSHEY. 

